Classroom curricula are the primary means by which the nation seeks to prevent adolescent substance use. There are now several decades of research identifying effective curricula for preventing, or at least delaying, substance use initiation. Historically, such curricula have not enjoyed widespread use; however, their prevalence is increasing as federal sponsors, such as the Safe and Drug Free Schools Program, have increasingly required their grant recipients to use curricula that are specified as effective by any of several national registries. There is now considerable empirical evidence linking the achievement of program effects to the fidelity with which teachers implement their curricula. However, there is also ample evidence suggesting that teachers tend to make substantial modifications to the curricula they implement. While teacher training has been shown to increase the fidelity with which teachers implement a curriculum (at least initially), we know very little about how implementation fidelity may alter over time. The primary aims of this study are to examine: (1) the relationship between the continued or sustained use of evidence-based curricula and the fidelity with which teachers implement them in the nation's middle schools; and (2) the moderating effects on this relationship of key organizational (e.g., administrative support, training) and teacher (e.g., motivation, curriculum understanding) characteristics. We will address these aims by deconstructing fidelity into 4 key components, namely differentiation, adherence, dosage, and delivery skill, and then examining the relationship between the sustained use of the 2 most prevalent evidence based curricula (Life Skills Training and Project ALERT) and the fidelity with which they are implemented. Our secondary aim is to validate our fidelity measures by comparing teachers' self-reports of fidelity measures with those of independent raters. Data for our primary aims will be drawn from the second NIDA funded School-Based Substance Use Prevention Programs Study, a nationally representative sample of prevention teachers in middle schools. Our secondary aim will use data from a Project Alert replication study. Understanding the relationship between sustained curriculum use and implementation fidelity will facilitate the development of more effective training programs for both novice and experienced implementers, ultimately improving program effects and thus reducing adolescent drug use. [unreadable] [unreadable]